Milan Gelnar

Molecular markers for gyrodactylids (Gyrodactylidae: Monogenea)from five fish families (Teleostei)

Thirty-one gyrodactylid species from five families of freshwater fish were examined and variable region V4 of the 18S small subunit ribosomal RNA gene and ribosomal RNA internal transcribed spacers ITS1 and ITS2 were sequenced. Both the V4 region and spacers ITS1 and ITS2 proved useful for gyrodactylid diagnosis. Sequences of these fragments exhibited interspecific variations and allowed clear determination at the species level. In some cases, the length of the ITS1 PCR fragment provided useful genetic markers. Species that yielded a short ITS1 fragment also showed distinct groupings in ITS2 and V4 sequences that were markedly different to sequences from species that contain a long ITS1. Repetitive sequences located in the ITS1 of Gyrodactylus gobii and Gyrodactylus vimbi accounted for some of the variations in length of PCR products. There was no evidence for intraspecific variation within these regions and short tandem repeats were not found in the other species studied. The number of polymorphic and intraspecific variations in nucleic acid sequences was low, therefore these variations did not affect species determination of gyrodactylids. Minor differences in the sequences between Western and Eastern European populations were detected for Gyrodactylus salaris/Gyrodactylus thymalli, Gyrodactylus teuchis and Gyrodactylus truttae, but these do not affect species diagnosis based on ribosomal DNA sequence. These results confirm the utility of both variable region V4 and the ITS as molecular markers for Gyrodactylus species.

MOLECULAR PHYLOGENY OF CONGENERIC MONOGENEAN PARASITES (DACTYLOGYRUS): A CASE OF INTRAHOST SPECIATION

Abstract Dactylogyrus species (Dactylogyridae: Monogenea) are a group of monogenean gill parasites that are highly specific to freshwater fish of the family Cyprinidae. Dactylogyrus species were sampled from 19 cyprinids and one percid collected in Europe. Using partial 18S rDNA and ITS1 sequences, a phylogeny of 51 Dactylogyrus species was reconstructed to investigate the patterns of parasite speciation and diversification. Three main Dactylogyrus lineages were recognized from all phylogenetic trees, that is, analysis of 18S rDNA alone and combined 18SrDNA and ITS1. The first lineage associates the Dactylogyrus species of Cyprinus carpio and Carassius auratus of the Cyprininae; the second associates Dactylogyrus species of the Gobioninae, Pseudorasbora parva of the Rasborinae, and Ctenopharyngodon idella of the Cyprininae; and the third associates Dactylogyrus species of the Leuciscinae and Alburninae and Barbus barbus of the Cyprininae. Our results suggest that the genus Dactylogyrus is of quite recent origin and that these three lineages separated from each other in a very short period of time. Host subfamily mapping onto the parasite tree inferred from analysis of the combined dataset showed that the Cyprininae could be plesiomorphic hosts for Dactylogyrus. Dactylogyrus parasites would have secondarily colonized the Percidae and representatives of the Leuciscinae, Alburninae, Gobioninae, and Rasborinae. Comparison of host and parasite phylogenetic relationships indicated that a very high number of parasite duplications occurred within two of the three Dactylogyrus lineages. Dactylogyrus diversification can be mainly explained by sympatric intrahost speciation events that seem to be correlated to strict host specificity. Moreover, the present study shows that the congeneric parasites speciating within one host tend to occupy niches within hosts differing at least in one niche parameter.

SPECIFICITY AND SPECIALIZATION OF CONGENERIC MONOGENEANS PARASITIZING CYPRINID FISH

Abstract Patterns and likely processes connected with evolution of host specificity in congeneric monogeneans parasitizing fish species of the Cyprinidae were investigated. A total of 51 Dactylogyrus species was included. We investigated (1) the link between host specificity and parasite phylogeny; (2) the morphometric correlates of host specificity, parasite body size, and variables of attachment organs important for host specificity; (3) the evolution of morphological adaptation, that is, attachment organ; (4) the determinants of host specificity following the hypothesis of specialization on more predictable resources considering maximal body size, maximal longevity, and abundance as measures of host predictability; and (5) the potential link between host specificity and parasite diversification. Host specificity, expressed as an index of host specificity including phylogenetic and taxonomic relatedness of hosts, was partially associated with parasite phylogeny, but no significant contribution of host phylogeny was found. The mapping of host specificity into the phylogenetic tree suggests that being specialist is not a derived condition for Dactylogyrus species. The different morphometric traits of the attachment apparatus seem to be selected in connection with specialization of specialist parasites and other traits favored as adaptations in generalist parasites. Parasites widespread on several host species reach higher abundance within hosts, which supports the hypothesis of ecological specialization. When separating specialists and generalists, we confirmed the hypothesis of specialization on a predictable resource; that is, specialists with larger anchors tend to live on fish species with larger body size and greater longevity, which could be also interpreted as a mechanism for optimizing morphological adaptation. We demonstrated that ecology of host species could also be recognized as an important determinant of host specificity. The mapping of morphological characters of the attachment organ onto the parasite phylogenetic tree reveals that morphological evolution of the attachment organ is connected with host specificity in the context of fish relatedness, especially at the level of host subfamilies. Finally, we did not find that host specificity leads to parasite diversification in congeneric monogeneans.

Biodiversity of parasites in a freshwater environment with respect to pollution: metazoan parasites of chub (Leuciscus cephalus L.) as a model for statistical evaluation.

This paper represents an attempt to evaluate the environmental indicative potential of the biodiversity of monogenean parasites using hierarchically structured species-abundance data. A logical set of statistical methods integrating standard diversity indices, a novel approach to quantitative analysis of cumulative species-abundance curves and species-abundance models was applied for this purpose. Applicability of biodiversity measures was demonstrated using experimental data from a 1-year study on the ecology of metazoan parasites of chub (Leuciscus cephalus) in one polluted and one control site in the Morava river, Czech Republic. Analyses at the component community level revealed a significant decrease in the number of parasite species with a more equal distribution of their abundances in the polluted site compared with the control site. In order to reach a better understanding of the changes, diversity of Monogenea as a dominant part of the community was further examined within categories of species created according to: (1) specificity of infection (specialists and generalists), (2) monogenean genera (Dactylogyrus, Gyrodactylus and Paradiplozoon) and (3) inhabited guilds (skin + fins, gills). Assemblages of specialists in the polluted site exhibited a significantly reduced species richness and unequal distribution of abundances. The opposite pattern was observed in the case of generalists. The influence of pollution was also reflected by the distribution of species abundances within communities of Dactylogyrus and Paradiplozoon, while no significant shift was identified in the genus Gyrodactylus.

Parasite communities of freshwater fish under flood conditions.

Abstract. The parasite communities of the freshwater fish species roach (Rutilus rutilus), bitterling (Rhodeus sericeus amarus) and perch (Percafluviatilis) were investigated during a major flood. Differences in parasite community structure due to changes in the host environment were expected. We therefore tested for differences in parasite species abundance and diversity as a consequence of the flood. Potential changes in parasite community structure due to seasonal influences were also considered. We found differences in the composition of parasite species and the proportion of ecto- and endoparasites in the three host species. The parasite community of roach was richer in species than those of perch and bitterling. Roach harboured more ectoparasite than endoparasite species. Parasite communities of both perch and bitterling were richer in endoparasite species and had a lower number of ectoparasite species. Parasite communities of the three different host species responded in different ways to environmental change. Considering all parasite species, no effect of either season or flood was found on the species diversity in either perch or bitterling. The flood caused an increase in the parasite species diversity in roach. For roach and perch, higher parasite abundance were found before the flood compared to after flood. However, no difference was found between the different seasons after the flood. By contrast, bitterling had the highest parasite abundance in the season after the flood. When analysing ecto- and endoparasites separately, a decrease in ectoparasite abundance was found in roach and perch, probably related to the flood, and due mainly to a decrease in monogenean species. A significant increase in the abundance of endoparasites was found in perch. In bitterling, the post-flood increase in ectoparasites was due to a high abundance of Gyrodactylus spp. We conclude that the parasite communities of the three fish species responded in different ways to the flood. This may be due to changes in the host life history strategy or in the immune response in conditions of stress.

Molecular phylogenetic analysis of the genus Gyrodactylus (Platyhelminthes: Monogenea) inferred from rDNA ITS region: subgenera versus species groups.

Analyses of small subunit ribosomal RNA gene sequences of representatives of major taxa of Monopisthocotylea were performed to identify the sister group of Gyrodactylus. Nuclear ribosomal DNA sequences from the complete internal transcribed spacer (ITS) region were used to infer phylogeny of 37 Gyrodactylus species and Gyrodactyloides bychowskii, Macrogyrodactylus polypteri and Gyrdicotylus gallieni, using maximum likelihood, parsimony and Bayesian inference. The genus Gyrodactylus appeared to be a monophyletic group in all analyses, based on the present data set. Within the genus, there were 3 major groups recognized by high bootstrap values and posterior probabilities. None of the 6 subgenera appeared to be monophyletic, and the most basal subgenus G. (Gyrodactylus) was paraphyletic. Characteristics of the excretory system of Gyrodactylus do not seem to be conservative enough to reveal subgenera within Gyrodactylus and we suggest abandoning existing subgenera as indicators of phylogeny. The grouping of species based on the morphology of the ventral bar and marginal hooks seems to have sufficient power to infer relationships between the Gyrodactylus species.

Local and regional influences on patterns of parasite species richness of central European fishes

Local, regional and global influences on the patterns of parasite species richness of 39 freshwater fish species from Central Europe were investigated. Host local abundance and host occurrence were considered respectively as local and regional factors, while host geographical range in longitude and latitude was considered as a global factor. Influences of size, ecology and behavior of hosts were also included in a comparative analysis using the independent contrasts method. We considered host habitat, host diet, host shoaling behavior and mobility. We found a positive relationship between local occurrence of fish and global range of their distribution. We confirmed previous findings showing the importance of host behavior and ecology on the variability of parasite species richness. Second, we showed how a global pattern, such as host geographical range, may affect the variability in parasite species richness through its effects on local abundance and distribution of hosts. A negative relationship between endoparasite species richness and host longitudinal range was found. This suggests that fish with eastern distribution live in the boundary of their distribution in Central Europe far from their center of distribution, which should also be characterized by a higher diversity of parasites.

Morphometric correlates of host specificity in Dactylogyrus species (Monogenea) parasites of European Cyprinid fish

We test the hypothesis that living on larger fish may impose constraints, i.e. the need to develop large attachment organs, related to the necessity to remain attached on large gills. For this, we compiled data on body size and morphometric measurements of attachment organs of 44 Dactylogyrus species (ectoparasites with direct life-cycle) from 19 cyprinid species. Nineteen dactylogyrid species were considered as specialists (infecting only 1 host species) and 25 as generalists (infecting more than 1 species). The lack of phylogenetic information lead us to perform comparative analyses using raw values and independent contrasts obtained by random phylogenies. Our results show that rich parasite communities are formed by specialists and generalists whereas poor communities are composed mainly of generalist parasites. Moreover, specialists are found on larger hosts, which may reflect a specialization on a predictable resource, as larger fish live longer and offer large gills for parasite colonization. Parasite specialization is shown to be linked with adaptation of attachment organs to their fish hosts. Two morphometric variables of the attachment organ, the total length of anchor and length of base of anchor, were positively correlated with host length for specialists.

The interaction between an introduced fish host and local parasite fauna: Neogobius kessleri in the middle Danube River

Parasite communities of introduced fish Neogobius kessleri Günther (Gobiidae) were studied at five localities in the Slovak section of the Danube River during 2002–2005. Thirty-three metazoan parasite species were identified. All fish were infected with at least two parasite species; most of the parasite species were generalists. At all sampling sites, high susceptibility to local parasites was observed. The parasite community was dominated by three parasite species: glochidia of Anodonta anatina, larval or subadult acanthocephalan Pomphorhynchus laevis, and larval nematode Raphidascaris acus. The infection of both A. anatina and P. laevis was affected by season and habitat type, with higher abundance in spring and more frequent occurrence of A. anatina in side channels and P. laevis in main river channels. At both the component and infracommunity levels, a more diverse parasite community was found in side channels. This habitat was dominated by actively transmitted parasites, whilst endoparasites were more abundant in fish from the main river channel. Larval stages of parasites dominated the endoparasite community at all sampling sites. The introduced N. kessleri was used as intermediate host for most of the recorded parasites, in some cases also as a paratenic host. Finally, the importance of gobies as suitable hosts for local non-native parasite species (Anguillicoloides crassus, Anodonta woodina, Hydrozetes lacustris) is discussed.

Seasonal occurrence and metrical variability of Gyrodactylus rhodei Žitňan 1964 (Monogenea, Gyrodactylidae)

The seasonal dynamics of Gyrodactylus rhodei, a monogenean ectoparasite of bitterling (Rhodeus sericeus), was studied from June 2000 to May 2001 in the Kyjovka River, Czech Republic. A negative relationship between prevalence and intensity of infection of G. rhodei and water temperature was found. Metrical variability of the hard parts of the parasite haptor was studied throughout the sampling season. A negative relationship between water temperature and the size of the hard parts of the G. rhodei haptor was evident in the measurements of the total length of the marginal hooks, the sickle length of marginal hooks, anchors, anchor point and root, the width of the ventral bar and the membrane processes. Sequences of the partial ITS (rDNA) of specimens collected during the cold and warm seasons were analysed. Sequences of all studied parasite specimens were identical and there was no evidence of intraspecific variability in the sequenced region.